The sole use of a gun is to throw a projectile. The earliest projectile was a stone thrown by the hand and arm of man—either in an attack upon an enemy or upon a beast that was being hunted for food. Both of these uses of thrown projectiles persist to this day, and during all time, from prehistoric days until now, every man who had a projectile to throw was steadily seeking for a longer range and a heavier projectile.
The man who could throw the heaviest stone the longest distance was the most powerfully armed. In the Biblical battle between David and Goliath, the arm of David was strengthened and lengthened by a leather sling of very simple construction. Much practice had given the young shepherd muscular strength and direction, and his longer arm and straighter aim gave him power to overcome his more heavily armed adversary.
Later, machines were developed after the fashion of a crossbow mounted upon a small wooden carriage which usually was a hollowed trough open on top and upon which a heavy stone was laid. The thong of the crossbow was drawn by a powerful screw operated by man power, and the crossbow arrangement when released would throw a stone weighing many pounds quite a distance over the walls of a besieged city or from such walls into the camps and ranks of the besiegers. This again was an attempt by mechanical means to develop and lengthen the stroke of the arm and the weight of the projectile.
With the development of explosives, which was much earlier than many people suppose, there came a still greater range and weight of projectile thrown, although the first guns were composed of staves of wood fitted together and hooped up like a long, slender barrel, wound with wet rawhide in many folds, which, when dried, exerted a compressive force upon the staves of the barrel exactly as do the steel hoops of barrels used in ordinary commercial life to-day.
This, the first gun, sufficed for a long while until the age of iron came. And then the same principle of gun construction was followed as is seen in that historical gun, the "Mons Meg," in the castle at Edinburgh. The barrel of that gun is made of square bars ofiron, placed lengthwise, and similar bars of iron were wrapped hot around the staves to confine them in place and to give more resisting power than was possible with the wooden staves and the rawhide hooping.
Thus, all during the age of iron, gun development went steadily forward. Every military power was always striving by the aid of its best engineers, designers, and manufacturers to get a stronger gun, either with or without a heavier projectile, but in every case striving for greater power. As a special development we find in March, 1918, the now famous long-range gun of the Germans, which was at that time trained upon Paris, where it successfully delivered a shell approximately 9 inches in diameter, punctually every 20 minutes for a good part of each day until the gun was worn out. This occurred after a comparatively small number of shots, probably not more than 75 in all. The rapid wearing out was due to the immense demands of the long range upon the material of the gun. The Germans in the shelling of Paris used three of these long-range weapons and 183 shells are known to have fallen in the city.
The Germans evidently calculated with great care and experience upon the factors leading up to this famous long-range type of gun, which had an effective shooting distance of approximately 75 miles, which range, in the opinion of our experts, it is now quite easy for an experienced designer and manufacturer to equal and excel at will. In fact, one would hesitate to place a limit upon the length of range that could be achieved by a gun that it is now possible to design and build. In this connection it is interesting to note that the great French ordnance works at Le Creusot in 1892 produced the first known and well-authenticated long-range gun, which was constructed from the design of a 12-inch gun, but bored down to throw a 6-inch projectile. And instead of the usual 8 miles expected from the flight of a 6-inch shell this early Creusot long-range gun gave a range of approximately 21 miles with a 6-inch projectile, using a 12-inch gun's powder charge.
Closely connected with the development of the gun itself, and a necessary element of the gun's successful use, is the requirement that the weapon itself be easily transported from point to point, where its available range and capacity for throwing the projectile can be made of maximum use. This requires a gun carriage which has within itself various functions, the primary one being to establish the gun in the desired position where it can be made most effective against the enemy. Then, too, the gun carriage must have stability in order to withstand, absorb, and care for the enormous recoil energies let loose by the firing of the gun. It is obvious that the force which propels the projectile forward is equal to the reacting force to the rear, and in order to care for, absorb, and distribute to the earth this reacting force to the rear the carriage must havewithin itself some very peculiar and important properties. To this end there is provided what is known as a "brake" which permits the gun, upon the moment of firing, to slide backward bodily within the controlling apparatus mounted upon a fixed carriage.
The sliding of the whole gun to the rear by means of the mechanism of the brake is controlled, as to speed and time, by springs, by compressed air, by compressed oil, etc., either all together or in combinations of two or three of these agencies; so that the whole recoil energy is absorbed and the rearward action of the gun brought to rest in a fraction of a second and in but a very few inches of travel. The strains are distributed from the recoil mechanism to the fixed portion of the carriage that is necessarily anchored to the ground by means of spades, which the recoil force of each shot sets more firmly into the ground, so that the whole apparatus is thus steadily held in place for successive shots.
In mobile artillery, again, rapid firing is a prime essential. The 75-millimeter gun of modern manufacture is capable of being fired at a rate in excess of 20 shots a minute—that is, a shot every 3 seconds.
Rarely however, is a gun served as rapidly as this. The more usual rate of fire is 6 shots a minute or 1 about each 10 seconds, and this rate of fire can be maintained in the 75-millimeter gun with great accuracy over a comparatively long period.
The larger guns are served at proportionately slower rates, until as the calibers progress to the 14-inch rifles, which have been set up upon railway mounts as well as on fixed emplacements for seacoast defense, the rate of fire is reduced to one shot in three minutes for railway mounts, and to one shot a minute for seacoast mounts, although upon occasions a more rapid rate of fire can be reached.
Under rapid fire conditions, the gun becomes very hot, owing to the heat generated by the combustion of the powder within the gun at pressures as high as 35,000 pounds per square inch or more, which are generated at the moment of fire. This heat is communicated through the walls of the gun and taken off by the cooling properties of the air. Nevertheless, the wall of the gun becomes so hot that it would scorch or burn a hand laid upon it. The rapid fire and heating of the gun lessens the effective life of the weapon, due to the fact that the hot powder gases react more rapidly on hot metal than they do upon cold metal; hence a gun will last many rounds longer if fired at a slow rate than if fired at a rapid rate.
It may be helpful to keep in mind throughout that the sole purpose of a gun is to fire a projectile, as was stated at the very beginning of this chapter. All other operations connected with the life of a gun, its manufacture, its transportation to the place where it is to be used, its aiming, its loading and all its functions and operations are bound up in the single purpose of actually firing the shot.
Consider now for a moment, the life of, let us say, one of the 14-inch guns.
In the great steel mills it requires hundreds and perhaps thousands of workmen to constitute the force necessary to handle the enormous masses of steel through the various processes which finally result in the finished gun.
From the first operation in the steel mill it requires perhaps as long as 10 months to produce the gun ready for the first test. During the 10 months of manufacture of one of these 14-inch rifles there has been expended for the gun and its carriage approximately $200,000. Of course, while it requires 10 months to make a final delivery of one gun after its first operation is commenced, it should be remembered that yet other guns are following in series and that in a well-equipped ordnance factory two and perhaps three guns per month of this kind can be turned out continuously, if required.
Remembering now that it requires 10 months to produce one such 14-inch rifle and that its whole purpose is to fire a shot, consider now the time required to fire this shot. As the primer is fired and the powder charge ignited the projectile begins to move forward in the bore of the gun at an increasingly rapid rate, so that by the time it emerges from the muzzle and starts on its errand of death and destruction, it has taken from a thirtieth to a fiftieth of a second in time, depending upon certain conditions.
Assuming that a fiftieth of a second has been taken up and that the life of a large high-pressure gun at a normal rate of firing is 150 shots, it is obvious then that in the actual firing of these 150 shots only three seconds of time are consumed. Therefore, the active life of the gun, which it has taken 10 months to build, is but three seconds long in the actual performance of the function of throwing a shot.
However, after the gun has fired its life of 150 shots it is a comparatively simple and inexpensive matter to bore out the worn-out liner and insert a new liner, thus fitting the gun again for service, with an expenditure of time and money much less than would be required in the preparation of a new gun.
As the size of the powder charge decreases, a progressively longer life of the walls of the bore of a gun is attained, so that we have had the experience of a 75-millimeter gun firing 12,000 rounds without serious effect upon the accuracy of fire. Large-caliber guns, such as 12-inch howitzers, with the reduced powder charge required for the lower muzzle velocities employed in howitzer attack, have retained their accuracy of fire after 10,000 rounds.
From the fact that when in action guns are served with ammunition, aimed, fired, and cared for by a crew of men carefully trained toevery motion involved in the successful use of the gun, it is most essential that the design and the material shall be such, both as to calculation in the design and as to manufacture in the material, as will insure the maintenance of the morale of the crew that serves the gun. Each man must be confident to the very last bit of fiber in his make-up that his gun is the best gun in the world, that it will behave properly, that it will protect him and his fellow soldiers who are caring for the welfare of their country, that it will respond accurately and well to every demand made upon it, that it will not yield or burst, that it will not shoot wild, but that it will in every respect give the result required in its operation.
To this end it has for generations been known that the requirements of manufacture of ordnance material, particularly for the body of the gun, are of the very highest order and call for the finest attainable quality in material, workmanship, and design.
It is well known and admitted that the steel employed in the manufacture of guns must be of the highest quality and of the finest grade for its purpose. It requires the most expert knowledge of the manufacture of steel to obtain this grade and quality. Until recently this knowledge in America was confined to the Ordnance officers of the Army and of the Navy and to a comparatively small number of manufacturers—not more than four in all—and only two of these manufacturers had provided the necessary equipment and appliances for the manufacture of complete guns.
Until 1914 the number of guns whose manufacture was provided for in this country as well as in the countries of Europe, excepting Germany, was very small. It might be stated that the sum total of guns purchased by the United States from the two factories mentioned did not exceed an average of 55 guns a year in calibers of from 3-inch to 14-inch, and that the stock of guns which by this low rate of increase of manufacture had been provided for us was pitifully small with which to enter a war of the magnitude of the one through which this country has just passed.
The two factories in question not having been encouraged by large purchases of ordnance material, as were similar industries in Germany, were not capable of volume production when we entered the war. But at the same time the gun bodies produced by these concerns at least equaled in quality those built in any other country on earth; so that while the big-gun-making art was in existence in this country and was maintained as to quality, it was most insufficient as to the quantity of the production available.
When the United States faced the war in April, 1917, arrangements were at once entered into to obtain in the shortest space of time an adequate supply of finished artillery of all calibers required by our troops and to get this supply in time to meet our men asthey should set foot on the shores of France. Many thousands of forgings for guns, and finished guns too, had been ordered by the allies of the few gun makers in this country; and these makers were, at the time we got into the conflict, fully occupied for at least a year ahead with orders from the French and English ordnance departments. All of this production was immediately useful and available for the combined armies of the allies, and so it was allowed to go forward, the forgings preventing a gap in the output of the finished articles from the British and French arsenals which were then using the semifinished guns made in the old factories in existence in this country in April, 1917.
Some idea of the volume of this production in this country will be gained from the following table showing material supplied to the allies between April, 1917, and the date of the signing of the armistice, November 11, 1918.
In supplying all of this material from our regular sources of manufacture in this country to the finishing arsenals of the allies we were but maintaining our position as a part of the general source of supply. The plan of the French and British ordnance engineers at the outbreak of the war in 1914 was to build their factories as quickly and as extensively as could possibly be done. By the time the United States entered the war all of these factories were in operation and clamoring for raw material at a rate which was far in excess of that which could be supplied by the home steel makers in Great Britain and France. Consequently their incursions into the semifinished ordnance material supplies in the United States were necessary. In sending these large quantities of our own materials abroad, when we needed them ourselves, we were distinctly adding to the rate and quantity of the supply of finished ordnance for the use of our own Army in the field as well as being at the same time of inestimable value to the allies. This was because the French and British had agreed to supply our first armies with finished fighting weapons while we were giving them the raw materials which they needed so badly.
The four gunmakers in America meanwhile were being expanded into a total of 19 makers. All of these 19 factories during the month of October, 1918, were practically in full operation. Many of them were producing big guns at a faster rate than that for which the plants had been designed. In the month of October, 1918, with 3 of the 19 factories yet to have their machine-tool equipment completed, there were produced 2,031 sets of gun forgings between the calibers of 3-inch and 9.5-inch, which is at the rate of upward of 24,000 guns a year. This figure, of course, does not indicate anything of thegun-finishing capacity of the country; yet this expansion may be contrasted to the fact that our supply of finished guns prior to 1917 amounted only to 55 weapons a year.
[9]Carriages, recuperators, and sights had to be added to these cannon to make them complete units ready for service.
[9]Carriages, recuperators, and sights had to be added to these cannon to make them complete units ready for service.
Our chain of gun factories, that were making this remarkable production, were built as follows:
One at the Watertown Arsenal, Watertown, Mass., near Boston, for the manufacture of rough machined gun forgings of the larger mobile calibers. This factory was entirely built and equipped on Government land with Government money and is splendidly able to produce rough machined gun forgings of the highest quality at the rate of two sets a day for the 155-millimeter G. P. F. rifles, and one set a day of the 240-millimeter howitzers.
At Watervliet Arsenal, Watervliet, N. Y., large extensions were made to the existing plant that had always been the Army's prime reliance for the finishing and the assembly of guns of all calibers, including the very largest. This plant was extended to manufacture complete four of the 240-millimeter howitzers each day, and two a day of the 155-millimeter G. P. F. guns.
At Bridgeport, Conn., there was constructed a complete new factory by the Bullard Engineering Works for the United States to turn out four 155-millimeter G. P. F. guns a day.
At Philadelphia, the Tacony Ordnance Corporation, as agents for the Government, erected complete a new factory officered and manned by experts well-trained and experienced in the difficult art of the manufacture of steel and gun forgings. On October 11, 1917, the grounds for this great undertaking had been merely staked out for the outline of the buildings. Seven months later, on May 15, 1918, the entire group of buildings, comprising a complete steel works from making the steel to the final completion of 155-millimeter gun forgings, was entirely erected at a cost of about $3,000,000. This difficult and rapid building operation was carried through successfully during the extraordinarily severe winter of 1917-18. On June 29, 1918, the first carload of gun forgings was accepted and shipped from this plant, so we have the marvelous enterprise of building a complete steel works from the bare ground forward to the shipment of its first forgings in a total elapsed time of only eight and one-half months.
At another, the works of the Midvale Steel Co. in Philadelphia, large extensions were made to enable some of the larger guns to be produced, to be finished later at the Watervliet Arsenal.
At the Bethlehem Steel Co.'s plant, Bethlehem, Pa., as early as May, 1917, orders were placed and appropriations allotted for expansions to this enterprise to enable a rapid output of a larger number of gun forgings and finished guns.
Large extensions were made at the works of the Standard Steel Works Co., Burnham, Pa., to increase their existing forging and heat treating facilities, so that at this plant two sets of 155-millimeter howitzers and one set of 155-millimeter gun forgings were produced each day.
At Pittsburgh, Pa., the plants of the Heppenstall Forge & Knife Co. and the Edgewater Steel Co. were extended so as to provide for the daily production at the first plant of forgings for one 3-inch antiaircraft gun and one 4.7-inch gun, and at the second plant of forgings for one 155-millimeter G. P. F. gun and one 240-millimeter howitzer per day.
At Columbus, Ohio, the Buckeye Steel & Castings Co. in combination with the works of the Symington-Anderson Co. at Rochester, N. Y., had their facilities extended to provide for the manufacture each day of six sets of forgings for the 75-millimeter guns.
At the Symington-Anderson Co. in Rochester, N. Y., there was provided a finishing plant for the 75-millimeter gun with a capacity of 15 finished guns per day.
At Erie, Pa., one of the most remarkable achievements in rapid construction and successful mechanical operation was performed by the erection of a plant that was commenced in July, 1917, and out of which the first production was shipped to the Aberdeen Proving Grounds in February, 1918. The American Brake Shoe & Foundry Co. built and operated this plant as agents for the Ordnance Department, and much credit is due them for their energy and organizing capacity.
It is doubtful if history records any similar enterprise in which guns were turned out in a plant seven months from the date of beginning the erection of the factory. This plant was laid out to manufacture 10 of the 155-millimeter Schneider-type howitzers a day, and before the signing of the armistice it had more than fulfilled every expectation by regularly turning out up to 15 howitzers a day, or 90 a week.
At Detroit, Mich., the Chalkis Manufacturing Co. adapted an existing plant, and additional facilities were erected for the manufacture of three of the 3-inch antiaircraft guns each day.
At Madison, Wis., the Northwestern Ordnance Co. erected for the United States an entire new factory, beautifully equipped for the manufacture of four guns a day of the 4.7-inch model.
At Milwaukee, Wis., the Wisconsin Gun Co. put up for the Government an entirely new works capable of finishing six 75-millimeter guns each day. The plants at both Milwaukee and Madison acquitted themselves very well and gave us guns of the highest quality.
At Chicago, the Illinois Steel Co. expanded existing facilities to produce more of the necessary electric furnace steel, which was forged into guns at several works producing gun forgings, both for the Army and Navy.
At Indiana Harbor, Ind., the works of the Standard Forgings Co., whose sole business had been the volume production of forgings withsteam hammers and hydraulic presses, were expanded to the enormous degree of producing each day 10 sets of gun forgings for the 155-millimeter howitzer and 25 sets a day for the 75-millimeter gun. It should be stated that this was a triumph of organizing ability and that this factory was one of our main reliances for these guns.
At Gary, Ind., the American Bridge Co. created what is perhaps the finest gun-forging plant in the world, comprising four presses from 1,000 tons to 3,000 tons forging capacity and all the other necessary apparatus for the production each day of two sets of 155-millimeter G. P. F. guns and the equivalent of one and one-half sets a day of the 240-millimeter howitzers.
At Baltimore, Md., the plant of the Hess Steel Corporation was enlarged from its peace-time capacity and caused to produce at three times its normal rate the special steels required for gun manufacture.
It will become evident that the collection of machinery, buildings, and equipment necessary to produce these guns in the short space of time required and at the rate of production stipulated, was an enormous task in itself. It required the production of vast quantities of raw materials and the congregating in one place of large numbers of men capable of undertaking the exceedingly intricate mechanical processes of manufacture. The success of this plan and its carrying out is due largely to the loyalty of the manufacturers who unselfishly came forward early in 1917 and agreed at the request of the Ordnance Department to turn over their plants, lock, stock, and barrel, to the requirements of the department; agreed also to undertake the manufacture of products totally unfamiliar to them; agreed likewise to lend all of their organizing ability and great material resources to the success of the plants which the United States found necessary to build in the creation of a new art, in new locations and in an extent theretofore undreamed of.
Steel, of course, and steel in some of its finest forms is the basis of gun manufacture. The word "steel" for the purpose of producing guns means much more than is ordinarily carried by the word in its everyday and most commonly accepted use. Only steel of the very highest quality is suitable for gun manufacture, as was indicated previously when attention was directed to the complete reliance which the operating crews must place in their guns and the severity of the uses to which the big guns are put.
Let us take a hasty trip through a big gun plant, watching the processes through which is finally evolved from the raw materials one of our hardy and efficient big guns.
Entering an open-hearth furnace building at one of our big gun plants, we find two large furnaces in which the raw materials arecharged. Each of these furnaces is 75 feet long and 15 feet wide, and in them in a shallow bath or pool lies the molten steel. The pool is about 33 feet long by 12 feet wide and approximately 2½ feet deep. This pool, or "bath" as it is termed, weighs approximately 60 tons and is composed of pig iron and well-selected scrap steel from previous operations.
The furnace is at all times during the operation of melting these raw materials in the bath kept at such a high temperature that the eye may not look within at the molten mass without being protected with blue glass or smoked glass, exactly as when looking at the noonday sun. The eye can see nothing in the atmosphere of the bath in which the steel is being melted and refined because the temperature is so exceedingly high that it gives a light as white as that of the sun.
After 12 or 15 hours of refining treatment in this furnace the metal is tested, analyzed in the chemical laboratory, and, if found to be refined to the proper degree, it is allowed to flow out of the furnace on the opposite side from that through which it entered. Flowing out of the furnace the entire charge of 60 tons finds its way into a huge ladle which is suspended from a traveling crane capable of safely carrying this great weight.
The ladle is then transferred by the crane to a heavy cast-iron mold which is built so as to contain as much of the 60 tons of molten metal as is required for the particular gun forging under manufacture.
The mold, which we have before us now on our imaginary trip through the gun plant, will provide an "ingot" from the molten metal that will be 40 inches in diameter and 100 inches high. On top of this ingot is a brick-lined so-called "sinkhead." This sinkhead is that portion of the molten metal that has been allowed to cool more slowly in the brick lining than the ingot does in the cast-iron mold proper. The ingot with the sinkhead will weigh approximately 60,000 pounds.
This sinkhead is to insure greater solidity to the portion of the ingot which is used for the gun forging. Only that part of the ingot below the sinkhead enters the forging. The sinkhead itself is cut off while hot under the press in a subsequent operation and afterwards remelted.
Next the ingot is placed under a 2,000-ton forging press which handles ingots up to 45 inches in diameter. There it is forged into a square shape after coming from the mold in an octagonal form. Previous to its being put under this press, however, a careful chemical analysis has been made of the ingot to determine that it is satisfactory for gun purposes, and then before being put under the press the whole ingot is heated in the charge chamber and fired either by a gas or oil flame.
VIEW OF LADLE, CONTAINING 60 TONS OF MOLTEN STEEL SUSPENDED FROM A TRAVELING CRANE.The ladle is receiving metal from the furnace and the crane is conveying the ladle to the mold.
VIEW OF LADLE, CONTAINING 60 TONS OF MOLTEN STEEL SUSPENDED FROM A TRAVELING CRANE.The ladle is receiving metal from the furnace and the crane is conveying the ladle to the mold.
VIEW OF LADLE, CONTAINING 60 TONS OF MOLTEN STEEL SUSPENDED FROM A TRAVELING CRANE.
The ladle is receiving metal from the furnace and the crane is conveying the ladle to the mold.
MOLTEN STEEL BEING POURED FROM LADLE INTO MOLD, WHICH IS OF HEAVY CAST-IRON CONSTRUCTION, AT THE TACONY ORDNANCE CORPORATION.Arrow points from letter A to a completed ingot from a mold. The brick-lined sink head is a part of the mold and is to insure greater solidity to the portion of the ingot which is used for the gun forging; only the part below the sink head entering the forging, the sink head itself being cut off hot under the press in a subsequent operation.
MOLTEN STEEL BEING POURED FROM LADLE INTO MOLD, WHICH IS OF HEAVY CAST-IRON CONSTRUCTION, AT THE TACONY ORDNANCE CORPORATION.Arrow points from letter A to a completed ingot from a mold. The brick-lined sink head is a part of the mold and is to insure greater solidity to the portion of the ingot which is used for the gun forging; only the part below the sink head entering the forging, the sink head itself being cut off hot under the press in a subsequent operation.
MOLTEN STEEL BEING POURED FROM LADLE INTO MOLD, WHICH IS OF HEAVY CAST-IRON CONSTRUCTION, AT THE TACONY ORDNANCE CORPORATION.
Arrow points from letter A to a completed ingot from a mold. The brick-lined sink head is a part of the mold and is to insure greater solidity to the portion of the ingot which is used for the gun forging; only the part below the sink head entering the forging, the sink head itself being cut off hot under the press in a subsequent operation.
Arrow points from letter A to a completed ingot from a mold. The brick-lined sink head is a part of the mold and is to insure greater solidity to the portion of the ingot which is used for the gun forging; only the part below the sink head entering the forging, the sink head itself being cut off hot under the press in a subsequent operation.
VIEW OF INGOT MOLD.
VIEW OF INGOT MOLD.
VIEW OF INGOT MOLD.
A 2,000-TON FORGING PRESS AT THE TACONY ORDNANCE CORPORATION PLANT.This press can forge ingots up to 45 inches in diameter. The ingot under the press is shown in a partly forged state. Note that the original octagonal shape of the ingot as it came from the mold has been forged down to a square shape and later will be forged into a round shape. After coming from the mold, the ingot has been subjected to a careful chemical analysis to determine its fitness for use as a gun barrel.
A 2,000-TON FORGING PRESS AT THE TACONY ORDNANCE CORPORATION PLANT.This press can forge ingots up to 45 inches in diameter. The ingot under the press is shown in a partly forged state. Note that the original octagonal shape of the ingot as it came from the mold has been forged down to a square shape and later will be forged into a round shape. After coming from the mold, the ingot has been subjected to a careful chemical analysis to determine its fitness for use as a gun barrel.
A 2,000-TON FORGING PRESS AT THE TACONY ORDNANCE CORPORATION PLANT.
This press can forge ingots up to 45 inches in diameter. The ingot under the press is shown in a partly forged state. Note that the original octagonal shape of the ingot as it came from the mold has been forged down to a square shape and later will be forged into a round shape. After coming from the mold, the ingot has been subjected to a careful chemical analysis to determine its fitness for use as a gun barrel.
This press can forge ingots up to 45 inches in diameter. The ingot under the press is shown in a partly forged state. Note that the original octagonal shape of the ingot as it came from the mold has been forged down to a square shape and later will be forged into a round shape. After coming from the mold, the ingot has been subjected to a careful chemical analysis to determine its fitness for use as a gun barrel.
A 9,000 TON HYDRAULIC FORGING PRESS IN THE PLANT OF THE MIDVALE STEEL CO.This press is needed for such large caliber guns as the 14-inch and 16-inch guns. The piece of forging under the press is armor plate and not a gun forging.
A 9,000 TON HYDRAULIC FORGING PRESS IN THE PLANT OF THE MIDVALE STEEL CO.This press is needed for such large caliber guns as the 14-inch and 16-inch guns. The piece of forging under the press is armor plate and not a gun forging.
A 9,000 TON HYDRAULIC FORGING PRESS IN THE PLANT OF THE MIDVALE STEEL CO.
This press is needed for such large caliber guns as the 14-inch and 16-inch guns. The piece of forging under the press is armor plate and not a gun forging.
THREE TUBES OF THE 155-MILLIMETER GUNS SUSPENDED AT FURNACE.Three tubes of the 155-millimeter guns suspended at furnace ready for heating and quenching to give them the necessary combination of hardness and toughness. The door of the furnace is open. The tubes remain in this furnace for perhaps eight hours at a temperature of 1,500° Fahrenheit or until a bright yellow color, uniform in every part.
THREE TUBES OF THE 155-MILLIMETER GUNS SUSPENDED AT FURNACE.Three tubes of the 155-millimeter guns suspended at furnace ready for heating and quenching to give them the necessary combination of hardness and toughness. The door of the furnace is open. The tubes remain in this furnace for perhaps eight hours at a temperature of 1,500° Fahrenheit or until a bright yellow color, uniform in every part.
THREE TUBES OF THE 155-MILLIMETER GUNS SUSPENDED AT FURNACE.
Three tubes of the 155-millimeter guns suspended at furnace ready for heating and quenching to give them the necessary combination of hardness and toughness. The door of the furnace is open. The tubes remain in this furnace for perhaps eight hours at a temperature of 1,500° Fahrenheit or until a bright yellow color, uniform in every part.
Three tubes of the 155-millimeter guns suspended at furnace ready for heating and quenching to give them the necessary combination of hardness and toughness. The door of the furnace is open. The tubes remain in this furnace for perhaps eight hours at a temperature of 1,500° Fahrenheit or until a bright yellow color, uniform in every part.
A TUBE FOR A 12-INCH GUN JUST OUT OF THE FURNACE, WHERE IT WAS TEMPERED AT WHITE HEAT AND IS NOW READY FOR QUENCHING IN THE PLANT OF THE MIDVALE STEEL CO.The gun tube is 41 feet long.
A TUBE FOR A 12-INCH GUN JUST OUT OF THE FURNACE, WHERE IT WAS TEMPERED AT WHITE HEAT AND IS NOW READY FOR QUENCHING IN THE PLANT OF THE MIDVALE STEEL CO.The gun tube is 41 feet long.
A TUBE FOR A 12-INCH GUN JUST OUT OF THE FURNACE, WHERE IT WAS TEMPERED AT WHITE HEAT AND IS NOW READY FOR QUENCHING IN THE PLANT OF THE MIDVALE STEEL CO.
The gun tube is 41 feet long.
TUBE OF A 155-MILLIMETER GUN BEING TURNED, PRIOR TO BORING, AT THE TACONY ORDNANCE CORPORATION PLANT.
TUBE OF A 155-MILLIMETER GUN BEING TURNED, PRIOR TO BORING, AT THE TACONY ORDNANCE CORPORATION PLANT.
TUBE OF A 155-MILLIMETER GUN BEING TURNED, PRIOR TO BORING, AT THE TACONY ORDNANCE CORPORATION PLANT.
TUBE OF A 155-MILLIMETER GUN IN A LATHE BEING BORED.The ingot out of which this tube was made, came from the mold in an octagonal shape and later was forged into a square shape and finally made round. It now, too, has the hole bored partially into it. Through this hole, ultimately, will pass the projectile.
TUBE OF A 155-MILLIMETER GUN IN A LATHE BEING BORED.The ingot out of which this tube was made, came from the mold in an octagonal shape and later was forged into a square shape and finally made round. It now, too, has the hole bored partially into it. Through this hole, ultimately, will pass the projectile.
TUBE OF A 155-MILLIMETER GUN IN A LATHE BEING BORED.
The ingot out of which this tube was made, came from the mold in an octagonal shape and later was forged into a square shape and finally made round. It now, too, has the hole bored partially into it. Through this hole, ultimately, will pass the projectile.
The ingot out of which this tube was made, came from the mold in an octagonal shape and later was forged into a square shape and finally made round. It now, too, has the hole bored partially into it. Through this hole, ultimately, will pass the projectile.
The forging press used for the larger caliber guns, such as 14-inch and 16-inch, is of a 9,000-ton weight capacity.
After the ingot forging has been reduced from squareness to a cylindrical shape under the press, it is allowed to cool, then taken to the machine shop, where it is turned and the hole through which the projectile ultimately will pass is bored into it. This hole is somewhat smaller than the diameter of the projectile, because in the finishing operation, when the gun is assembled finally and put together, the hole must be within one-one-thousandth of an inch of the diameter required, which is all the tolerance that is allowed from the accuracy to which the projectiles are brought. Otherwise the accuracy of the gun in firing would be injured and the reliability of its aim would not be satisfactory.
During all of these operations with the ingot, the steel is largely in the soft condition in which it left the forging press. As is well known, steel is capable of taking many degrees of "temper." Temper is an old term that no longer is quite descriptive of the condition desired or obtained, but it is sufficiently expressive of the condition desired for the purposes here. This condition is one of a certain degree of hardness—greater than that ordinarily carried by the soft steel—combined with the greatest obtainable degree of toughness. This combination of hardness and toughness produced to the proper degree resists the explosive power of the powder and also causes the wear on the gun in firing to be diminished and made as slight as possible.
To effect this combination of hardness and toughness it is necessary to take the bored and turned tubes of the guns and suspend them by means of a specially made apparatus in a furnace where they are heated for a period of perhaps eight hours to a temperature of approximately 1,500° F. or a bright-yellow color, uniform in every part of the piece.
After being subjected to this treatment for the time mentioned, the tube is then conducted by means of a traveling crane apparatus to a tank of warm water in which it is dipped and the heat rapidly taken from it down to a point of practically atmospheric temperature. This "quench" as it is called, produces the required degree of hardness called for by the ordnance officers' design; but the piece has not yet got the required degree of toughness. This toughness is now imparted to the hard piece by heating it once more in another furnace to a temperature of approximately 1,100° F., or a warm rosy red, for a period of perhaps 14 hours. From this temperature, the piece is allowed to cool naturally and slowly to the atmospheric temperature.
The ordnance inspectors at this point determine whether the piece has the required properties in a sufficient degree, by cutting from thetube a piece 5 inches long and ½ inch in diameter. The ends of this piece are threaded suitably for gripping in a machine. The piece is then pulled until the half-inch stem breaks. The machine registers the amount of force required to break this piece and this gives the ordnance engineer his test as to the degree of hardness and toughness to which the piece has been brought by the heat treatment processes just described.
A satisfactory physical condition having been determined by pulling and breaking the test pieces described, the whole forging is sent to the finishing shop where it is machined to a mirror polish on all its surfaces. The diameters are accurately measured and the forgings assembled into the shape of a finished gun.
In this process there is required a different kind of care and accuracy. Up until this time the care has been to provide a metal of proper consistency and quality. From this point forward the manufacture of a gun requires the machining and fitting of this metal into a shape and form so accurate that the full strength of the gun and the best accuracy of fire may be attained.
To explain how and why hoops are placed upon the gun tubing and how the various hoops are shrunk from the outside diameter of the gun will require a few lines.
Cannon are made of concentric cylinders shrunk one upon another. The object of this method of construction is twofold. The distinctly practical object is the attainment throughout the wall of each cylinder of the soundness and uniformity of metal which is more certainly to be had in thin pieces than in thick ones; the other object is more closely connected with the theory of gun construction.
When a hollow cylinder is subjected to an interior pressure the walls of the cylinder are not uniformly strained throughout their thickness, but the layer at the bore is much more severely strained than that at the outside. This can be readily seen if we consider a cylinder of rubber, for example, with a bore of 1 inch and an exterior diameter of 3 inches, which are about the proportions of many guns. If we put an interior air pressure on the cylinder until we expand the bore to 2 inches, the exterior diameter will not thereby be increased 1 inch. But supposing that it were increased as much as the bore, that is, 1 inch, we would have the diameter, and therefore the circumference, of the bore increased 100 per cent, and the circumference of the exterior increased 33⅓ per cent. That is, the layer at the bore would be strained three times as much as that at the exterior, and the interior layer would commence to tear before that at the exterior would reach anything like its limit of strength. The whole wall of the cylinder therefore would not be contributing its full strength toward resisting the interior pressure, and there would be a waste of material as well as a loss of strength.Let us now consider, instead of our simple cylinder, a built-up cylinder composed of two concentric ones, the inner one of a bore originally a little greater than 1 inch, and the outer one of exterior diameter a little less than three inches, originally; so that when the outer one is pressed over the inner one (its inner diameter being originally too small for it to go over the inner one without stretching) the bore of the inner one is brought to 1 inch, and the exterior of the outer one to 3 inches. We now have a cylinder of the same dimensions as our simple one, but in a different state; the layers of the inner one being compressed and those of the outer one extended.
If now we commence to put air pressure on the bore, we can put on a certain amount before we wipe out the compression of the inner layer, and bring it to a neutral state, and thereafter can go on putting on more pressure until we stretch the inner layer 100 per cent beyond the neutral state, as before; which would take just as much additional pressure as the total pressure which we employed with our simple cylinder. We have therefore gained all that pressure which is necessary to bring the inner layer of our built-up cylinder from its state of compression to the neutral state. If we have so proportioned the diameter of junction of our inner and outer cylinders and so gauged the amount of stretching required to get the outer one over the inner one that we have not in the process caused any of the layers of the outer one to be overstrained, the gain has been a real one, attained by causing the layers of the outer cylinder to make a better contribution of strength toward resisting the interior pressure. This is the theory of the built-up gun.
The number of cylinders employed generally increases, up to a certain limit, with the size of the gun, practical considerations governing; and the "shrinkage," or amount by which the inner diameter of the outer cylinder is less than the outer diameter of the one which it is to be shrunk over, is a matter of nice calculation. Roughly speaking, it is about one and one half one-thousandths of an inch for each inch of diameter, varying with the position of the cylinder in the gun; and its accurate attainment, throughout the length of the cylinder of a large gun, is a delicate matter of the gun-maker's art and the machinist's skill.
The method of assembly is to have the cold tube set upright and prepared for a circulation of water within the bore of the tube to keep it cool. Then the hoop, whose inside diameter is smaller than the outside diameter of the tube on which it is to be shrunk, is measured and carefully heated to a temperature of approximately 450° F., or just about the temperature of a good oven for baking or roasting. This mild temperature so expands the material in the hoop that the difference of diameter is overcome and the hot hoop is expanded to a larger inside diameter than the outside diameter of thecold tube on which the hoop is to be placed. Next the hot, expanded hoop is placed in position around the breech end of the tube, and slowly and carefully cooled, so that in contracting from the high temperature to the low ordinary temperature, the hoop shrinks toward its original diameter and thus exerts an inclosing pressure or compressive strain upon the breech end of the tube.
Now when the gun is fired the tube tends to expand under the pressure and this expansion is resisted, first by the compressive force exerted by the shrunken hoop and later by the hoop itself, so that the built-up system is stronger and better able to resist the explosive charge of the burning powder than would be the case if the gun were made in one piece and of the same thickness of metal.
This brief explanation will show why so many pieces are provided for the manufacture of the finished gun and the reason for the large number of machine tools and machining operations necessary in order to carry forward the manufacture of the finished article. Sometimes one or more of the outer cylinders are replaced by layers of wire, wound under tension.
Both our 4.7-inch gun, model 1906, with which our troops have been equipped for a long time and which throws a projectile weighing 45 pounds a distance of about 6 miles, and the French 75-millimeter (2.95-inch) gun, successfully used by the French since 1897, were designed to be drawn by horses, and the guns are best used when drawn by teams of 6 or 8 horses. As the horse has a sustained pulling power of only 650 pounds, it is obvious that the weight to be drawn by the team of 6 horses must not be more than 3,900 pounds. So there is every incentive for making mobile artillery of this kind as light as possible, consistent with the strength required for the work to be done. Thus the pulling power of the horse coupled with his speed has been the limiting factor in the design and weight of mobile field artillery.
As one of our foremost United States ordnance engineers once said, "the limited power of the horse is what has governed the weight of our artillery," and that "if Divine Providence had given the horse the speed of the deer and the power of the elephant, we might have had a far wider and more effective range for our mobile artillery."